Numerically controlled machine tools used preset tools carried in a tool storage magazine and a tool changer interchanges these tools as desired with the previously used tool in the tool spindle. Due to the numerical control the machine runs almost automatically with a minimum amount of supervision. The number of tools for use in the machine tool has gradually increased over the years in order to provide greater flexibility of machining capabilities to the machine tool. In some machine tools the tool changer had to be retracted in two different dimensions to a relatively stationary tool storage magazine before a tool interchange could be effected. This wasted considerable time during the total machining cycle.
A number of machine tools required that the operating spindle retract in only a single dimensional path to a tool interchange position. Where the operating spindle moved in two dimensions, this presented difficulty that the tool storage magazine had to move in one of those two dimensions so as to be available for the tool change function. When only 15 to 20 tools, for example, were used, the weight of the tool storage magazine was not significant. As the number of tools increased to 40 or 50 tools, for example, two factors rapidly increased, namely both the total weight of the tool magazine and the fact that the length of the tool magazine usually meant considerable rear overhang thereof. When the machine tool was attempted to be used with only about half of the tool sockets in the magazine occupied, this could cause a large unbalance condition to exist during movement of the magazine. At some times the weight could all be on the front of the magazine and at other times all on the rear. This would cause large changes in the moment on the support for the tool magazine which caused an undesirable deflection in the position of the tip of the tool in the operating spindle. This destroyed the machining accuracy of the machine tool.
Some prior art machine tools utilized counterbalances of either the weight type or fluid pressure type to attempt to eliminate this changing problem. Other machine tool manufacturers ignored the problem and made no provisions for the deflection caused by the change of moment.
Accordingly, the problem to be solved is how to accommodate the shifting weight of a moving tool storage magazine so that this shifting weight and concomitant change of moment does not materially affect the accuracy of the machine tool.